The Plasma Membrane essays

The Plasma Membrane essays The plasma membrane consists of 40 percent of lipid molecules and 60 percent of proteins. It plays a very important role in living organisms, in which one of its main functions is to act as a barrier between the internal and the external environment of each cell. Not only that, but it also controls the chemical reactions of a cell. In 1935, Davson and Danielli suggested that 40 percent of the lipid molecules are arranged in a lipid bilayer. Each phospholipid molecule consists of a glycerol molecule linked to two long chain fatty acids and a phosphate group or phosphate head. The lipid bilayer forms due to the hydrophobic and the hydrophilic nature of the phospholipid. The polar head or phosphate group is hydrophilic or water loving and the two fatty acid tails are hydrophobic, or water hating. The bilayer is therefore arranged in order for the fatty acids to exclude as much water as possible their structure. With improvements in technology (improvements in electron microscopy), a more detailed structure of the cell plasma membrane was laid out. The two scientists, in 1972, by the name of Singer and Nicolson, suggested that the membrane is a fluid structure and is always moving. They put forward the idea of the fluid mosaic model of the membrane. This suggests that there is a lipid bilayer, however, apart from that there is a mosaic or an irregular distribution of different sized proteins that span the membrane as well. There are three different types of proteins that span the cell surface membrane. The first one is the extrinsic protein. This protein is situated only on one side of the membrane. The intrinsic proteins or channel proteins span the whole membrane, covering both the sides of it. The third protein is the Glycoprotein. This protein has a different structure compared to the i...